I have a dilemma for my user created (original) High Fantasy setting. I have every zone, NPC, region and it's potential creatures all designed and solid. It's been a long running RP over Forums for a long time. I'm not lacking in story or background or how to tell said story. I am telling said story over a 'Virtual Tabletop' which I wont advertise on here. Suffice to say it allows me to physically build my maps and encounters with tokens and tiles and such. To pre-build the next leg or 5 of their journey. It's immersive...and they love it so far.

My problem comes from being a semi fledgling Dungeon Master and having no idea how to go about allowing them freedom of going where they wish and keeping the creatures they may encounter in any given area static with their level. Even with the full DMM and MM at my fingertips, I can't find a way (that I understand) to take a set of encounters I pre-built for them to go through at level 4, and turn them into level 6 encounters because they went a different path and will later arrive at said encounters.

I'll try and elaborate without rambling.

I originally thought they would go the following route:

Greater ForestStarter - Lesser Forest - Plains - Mountains

I built encounters to their EXP Threshold to make sure they had smooth leveling experiences as they went through. Well the above plan didn't go as I thought and they'll be going north straight to the mountains first as they seemingly pose the most intrigue to them. I have NO problem with this....but now I have an entire map of encounters built for level 6 that need to be level 4. No where can I find an equation or chart on how to alter creatures from the Monster Manual (MM) and make them higher or lower to fit my exp budget needs for them. 4E had an online monster creator and easy methods of making my own. 5E? Not so much.

I don't want to railroad my players into a linear adventuring experience if I don't have to. What are some suggestions to encounter building encounters that are easily changeable either up or down pending player character choice?

4 Answers
4

When I run sandbox games, I tend to divide the world into regions of general power; I start the players off in a low threat zone, full of mudcrabs, rattata, and the occasional goblin. Then, in universe, I tell the players what areas are safe. Rumors in the bar that the road to Harborhead has been having some bandit troubles. The city watch warning them as they leave town to take the left fork, not the right one, because the Ghostgate is full of terrifying spirits. A traveler who explains he and his whole town had to pick up and leave because a dragon took up residence in the mountains to the north. These hints allow the players to decide how much they're willing to risk; the loot and XP for taking out that dragon will be incredible, but it's very likely to roast them alive on the first round.

It sounds like you've played 4th edition in the past, which had a fairly strict power curve. 5th edition actually works even if the characters aren't at the same level as their opponents, helped by the fact that there isn't as big a difference between low and high level characters. Still, you and your players may have some habits to break.

As players, they need to learn how to pick their battles, estimating which fights they can win and setting things up to give them a leg up. They also need to learn when to retreat and back off. Some fights aren't winnable, for reasons nothing to do with levels. As a DM, you need to learn to foreshadow encounter difficulty clearly. (Honestly if you feel like you haven't made something clear, it's okay to drop out of character for a moment. "You can totally fight the dragon today if you want, but you guys should know I set him up to be a level twenty battle and I'm going to play him that way. If you beat him though, his hoard and XP will be on the same scale.")

5th edition plays to a slightly different tune than 4th, but for a sandbox game like yours, it should be an easier one to dance to.

While I agree with the general thrust of other answers i.e. if the PCs are stupid enough to go into "the deep dark mountains from which none have ever returned" before they are ready then the deserve what they get. But 5th edition provides plenty of guidance for scaling encounters - scaling monsters is not (necessarily) part of it (p.56-58 of the basic rules).

Scalability

First off, 5th edition is much more forgiving on different power levels that earlier editions - low CR monsters will still do damage to higher level PCs - they are much less likely to kill them outright but can attrit them to death in the long term.

This is the domain of the XP Thresholds by Character Level table (DM Basic p56). Study it, love it, understand it or ... just go by these rules of thumb:

At a given level the ratio of Medium, Hard and Deadly encounter budgets to Easy budgets is 2, 3 and 4.5. That is, if you double an Easy encounter it becomes Medium, if you double a Medium encounter it becomes (almost) Deadly (more or less).

From 5th through 20th, each level is about 1.2x the level below or 1.4x 2 levels below (again more or less - this is not an exact science).

Specifically, for 4 versus 6, Deadly and Hard encounters are now Easy, Medium and Easy encounters are now Trivial. So, you need to boost these encounters by adding about 40% more effective XP than you had before.

The easiest way to do this is to add more monsters, not to fiddle with the monsters you have:

For a 1 and 2 monster encounters, add a very low CR companion - they don't add much XP themselves but the multiply the effect of the main antagonist by dividing the party's resources.

For a 3-6 monster encounter, add 1 more of the same

For a 7+ monster encounter, add about 25-33% more of the same.

Another way is to scale up the hit points of the monsters - this means each encounter will use up more resources of the party (since the monsters last longer).

2. Pacing

It is assumed that the PCs will start the day fresh and have 2 short rests per day and gives a budget for how mach XP of encounters they should have in each day (the Adventuring Day XP table p.57) - roughly split into thirds to match their rests. This means that they will be at their best at the beginning of the first third and at their worst at the end of the third.

As well as or instead of tweaking each encounter, simply throw more encounters at them in each "shift". Done consistently, this gives the "spike" damage types (Wizards, Sorcerers, Warlocks) a dilemma about when to burn through their limited resources and allows the "consistent" damage types to shine. It also forces the "support" classes to use more of their resources in things like healing.

As DM you decide how the goblins (say) react to an incursion - to reduce difficulty they can adopt a passive defense - to increase it they can launch their own S&D missions. The latter means that the PCs cannot rest when they want - only when you want. It improves verisimilitude too since, in the real world, if you go poking about a wasp's nest the wasps do something about it.

3. Situation

You can modify the encounters by giving the monsters tactical advantages. Some examples include cover, traps and other hazards on the field that the monsters know about and take advantage of, surprise, attacking the party during a long or short rest; this may catch some asleep or without armour and also buggers up their pacing.

Advice

It is generally simpler to make an encounter harder than easier (add another monster) so aim for where the PCs are (they aren't going to go backwards) and beef it up as needed.

Alternatively, when constructing an encounter, write it down for say Level 4 and make notes on what to add to make it L6 and L8. For example:

D&D 5e is a finely-tuned machine for not caring in the least about keeping encounters static to the PCs' level. If you're coming from a game where keeping encounter difficulty matched to the PCs is critical, this might be somewhat alien, but it is true nonetheless. This is why there are no guidelines or rules for how to "level up" an encounter.

(Well, I may be overstating "finely-tuned" — but the point is that the game is designed so that you don't have to do what you're assuming you do.)

There are two ways for upping the difficulty of an encounter:

Add more monsters

Replace them with harder monsters

That's it.

Why isn't there more support for tuning encounters?!

D&D 5e is designed deliberately to eliminate the DM's monster treadmill. You don't have to be constantly finding new monsters in order to maintain the same level of challenge.

It's also designed so that it's easy to avoid railroading, but making encounter-turning unnecessary.

The design principle of bounded accuracy keeps PCs from ever completely outclassing an opponent, making monsters that they met at 1st level still relevant many levels later. This means you won't have to stop using monsters as the PCs level — instead of your palette of creatures staying small or even shrinking as they level, your palette of creatures grows upward on top of the solid base of low-powered creatures.

But its' more than bounded accuracy — 5e expects you to use a variety of encounter difficulties. This frees you to decide what is in the world (as you already have), and then just let the PCs roam as they will. What happens then is that some of the encounters are easy for the PCs. That's okay though, because tromping an encounter that would have been very hard a few levels back is fun. There is certainly fun in having knife-edge encounters, but not every encounter needs to be knife-edge balanced.

How to use encounters in a sandbox

Just put them wherever you like†. Let the PCs run into them.

The speed of easy encounters means that they won't get boring, and they'll be able to move more quickly — as makes sense for a group that is more powerful than the local dangers.

Difficult encounters will especially challenge them, and they may have to back off and take a different route. This is also something that makes sense — don't go into the Forbidden Forest when you're still a group of novices! Make sure they know that deciding to back off is something they will have to judge, as they may also be conditioned by a non-5e game to trust that encounters will never be "too" hard.

† "Wherever you like" doesn't mean "random." Just throwing things randomly into the world defeats the purpose of a sandbox — if the world is random, the players have just as little ability to carve their own destiny as in a railroad, and therefore only an illusion of agency. Place encounters based on locations that fit their difficulty; based on what sort of critters are native to the region; based on factions in the region. One very useful placement technique is to designate areas to have certain difficulty levels (regardless of the PCs' levels), thus creating "easy", "hard", "medium hard" areas, and so on. Add some variation in difficulty within these regions, and perhaps some means of dynamically generating fitting unplanned encounters, and the world will come alive for the players.

Broadly speaking, don't plan the sandboxes encounters by level, plan them by the internal logic of the setting. Put the responsibility on finding a level-appropriate path through it on the players.

Then just roll with it. If they're 6th level then let them enjoy being 6th level and steamrollering some 4th level opponents. If they encounter 10th level opponents, well, they should have scouted out the area first. That's what sandboxes are all about. If they HAVE to go a certain route then what you have is not a sandbox.